The proposed studies are designed to develop a methodology for comparison of pain intensity and pain reduction in pain patients and to specifically compare and assess pain reductions produced by graded doses of fentanyl and by different parameters of somatosensory stimulation. The latter are designed to activate opiate and non-opiate mechanisms of pain reduction. The project is divided into two main sections. The first section will simultaneously compare graded doses of fentanyl on experimental pain produced by 43-50 degreesC temperature stimuli and on different types of clinical pain and on the sensory and affective dimensions of these types of pain. This project serves to develop a reference standard for analgesia in pain patients and to determine the possible differential or consistent effects of fentanyl on experimental pain and different types of clinical pain. The second section will characterize and compare the relative magnitudes, time course, and general mechanism of pain reductions produced by 3 modes of TENS in low back pain patients and in myofascial pain dysfunction patients. These commonly used modes of TENS include 1) conventional high frequency (100H2), low intensity , 2) low frequency, high intensity ("acupuncture-like"), and 3) brief intense. This combination of projects should provide a relatively quantitatively accurate characterization and comparison of pain and pain reductions produced by common clinical treatments for chronic pain. The project also should help elucidate the parameters of pain reduction and the general mechanisms by which these treatments work.